Process for manufacturing form board for casting concrete



Patented Dec. 9, Ei hth PROCESS FOR MANUFACTURING FORM BOARD FUR CASTING CONCRETE John Holger Roseuquist, Alfredsheni, and Anders Wilhelm Westling, Enebyberg, Sweden, assignors to Aktieholaget Statens Skogsindustrier, Stockhoim, Sweden, a corporation of Sweden No Drawing. Application January 21, 1955 Serial No. 483,438

Claims priority, application Sweden January 26, 1954 6 Claims. (Cl. 92-40) This invention concerns the manufacture of oil-hardened weod fibre board, and more particularly the invention relates to a process for the manufacture of oilhardened wood fibre board suitable for use as form board or shuttering in the casting of concrete for building purposes and similar purposes.

When casting concrete with the help of wooden forms the surface of the concrete is always rough and must therefore be subjected to aftertreatment consisting in the application of plaster or the like which entails considerable work and heavy costs. In order to remove this drawback, in place of Wood, forms of sheet iron, oilhardened board and specially treated plywood have also been used.

Thus, when employing plywood for this purpose it has been treated with a plastic lacquer so that the wood receives a protective coating by Which means the alkali prevented from attacking the wood in the concrete is itself. Plywood treated in this manner is an excellent material for forms, giving fine concrete surfaces and having satisfactory strength and a long life, but on the other hand, it is expensive to produce.

The object of the invention is to provide a simple and convenient method for the manufacture of a type of hard oil-hardened fibre board which is especially adapted to be used as form board or shuttering in the casting of concrete.

For this purpose, according to the invention, the fibre board during the actual process of its production is uniformly impregnated with a hardenable oil and is provided with a layer of a plastic covering the surface thereof which is intended to come into contact with the concrete, said layer being alkali-resistant and impermeable to water, thus protecting the board against attack of the alkali in the concrete. In this process, the addition of the oil and the plastic takes place at a stage at which the fibre material has been felted into a web and still forms a wet fibre felt which is subsequently subjected to pressing against a polished plate.

In conformity with the foregoing, the process according to the invention comprises applying to one face only of the wet fibre felt a hardenable oil and also an alkaliresistant plastic, and then subjecting the felt to high pressure at increased temperature against a polished plate on the side of the felt provided with said agents, while maintaining acid reaction at least prior to completion of the pressing step, the amounts applied and the mutual viscosities of the oil and the plastic being such that in said pressing operation the heardenable oil is caused to flow into and become homogeneously distributed in the fibre felt throughout its entire thickness simultaneously driving out water present in the felt through the non-impregnated face thereof, whereas the plastic re mains at the surface of the board or in the topmost fibre layer forming a cohesive water-impermeable, alkaliresistant coating on the fibre board, whereupon the board is subjected to a hardening at suitable temperature.

so-t reated fibre board has excellent properties as form board in the casting of concrete and is essentially superior to that obtained in the customary manner and merely oil-hardened.

As examples of suitable viscosity values for the hardenable oil to enable to to fulfil the foregoing requiremerits, viscosities of the order of 200-800 cp. at 20 C. may be mentioned. For the plastic the viscosity should lie above 5000 cp. at 20 C., but is preferably considerably higher. The said value refers to low condensation products of comparatively high fluidity, but the con-densation may also be carried on so far that the condensate is obtained as a very viscid fluid or even as a solid powder which is suspended in a liquid and is applied to the fibre felt in this form.

Examples of suitable hardenable oils are linseed oil and alkyds of the same, tall oil and esters and alkyds of the same, for example tall oil modified with maleic acid anhydride or phthalic acid anhydride and esterified with glycerol, various plastic materials or combination of plastics, also Chinese wood oil and asphalt, or mixtures of the abovementioned substances.

Suitable plastics are thermosetting resins, such as phenol-formaldehyde resins, urea-formaldehyde resins, melamine-formaldehyde resins and mixtures of said resins, further thermoplastic materials, such as polyvinyl chloride, polystyrol etc. Especially favourable results have been obtained with co-condensates of urea-formaldehyderesins and melamine-formaldehyde resins which in solution have been condensed so far that the product is water-insoluble and is obtained as a powder but which can still be considered incompletely condensed. Other suitable examples are cation-active urea-formaldehyde resins.

The application of the hardenable oil and the plastic -to the fibre felt may take place in any suitable manner, either together or each per se separately. Preferably the hardening oil is supplied in the form of an aqueous emulsion which, for obtaining an acid reaction in the pressing operation, suitably may be prepared with the use of ammonium compounds as emulsifiers. The plastic may suitably also be applied in the form of a dispersion, i. e. as an emulsion or a suspension. Determining for the property of the plastic to remain or be retained on the surface of the fibre board or in the upper layer thereof is, in addition to its viscosity, also to a certain extent the particle size of the plastic when in suspension or emulsion. According to circumstances, the particle size may be within the ranges 5100,u, for example.

According to a manner of working, the oil and the plastic are applied simultaneously in the form of an aqueous emulsion of the oil which has been prepared with the use of an ammonium compound as emulsifier and in which emulsion the plastic has then been suspended. As indicated above, the impregnating oil and the plastic may also be applied separately, in which case the oil is suitably added in the form of an aqueous emulsion prepared with an ammonium compound as emulsifier, the resin being applied in the form of an aqueous emulsion or a suspension in water prepared by suspending resin powder in water or by precipitating a soluble resin from water, in both cases by the aid of a dispersing agent, for example an alkali soap, in order not to obtain too large resin particles.

The application to the fibre felt or web of the oil and the resin is preferably effected by spraying with nozzles in the board machine or immediately after the last pair of rolls of the board machine.

The amount of oil required to obtain the desired effect on the fibre board is suitably within the ranges of from about 3% to 12% by weight, based on the dry weight of The amount of the resin may suitably be within the ranges of from about /2 to preferably within the ranges 1.5-5%.

After the application of the oil and the resin to the fibre felt, the latter is subjected to a pressing suitably at a pressure of 50 kg./cm. and a temperature of 130- 200 C. for a period of from about 6 to minutes, for example, whereby an impregnation of the fibre felt and formation of an alkali-resistant coating layer on the surface of the fibre board takes place, as indicated above. The fibre board thus obtained is then subjected to a hardening for a sufiicient time, for example from about 1 hour to 12 hours, suitably at a temperature of 150-200 C.

As examples of the application of the process according to the invention the following may be mentioned.

Example 1 For the manufacture of form boards or shutterings provided with one outer layer consisting of a co-condensate of equal parts of urea-formaldehyde resin and melamineformaldehy-de resin while using glycerol esterified tall oil as a hardening impregnating oil, the following procedure may be applied. I

In 40 parts water 5 parts water-soluble urea-formaldehyde resin and 5 parts water-soluble melamine-formaldehyde resin are dissolved, whereupon 1 part concentrated acetic acid is added. The solution is stirred strongly at 20 C. for 5 hours and is then neutralized to pH=7, whereupon a suspension of mixed resins in the form of white, fine water-insoluble grains having a particle size Within the ranges 550 and a melting point of 100150 C. is obtained.

This suspension is then mixed with an aqueous emulsion of the glycerol-esterified tall oil containing ammonium phthalate as the emulsifier. After dilution with water to a suitable volume, the mixture is applied to the web with the help of a nozzle device. Owing to their size the resin grains remain at the surface of the fibre felt whereas the oil emulsion immediately penetrates into the web to some extent.

The amounts of oil and resin applied are 6-10% and 1.55%, respectively, based on the dry weight of the fibre felt.

The fibre felt which has been thus treated is then subjected to high pressure at a temperature of 150-200 C., as indicated above, whereupon the resin grains immediately flow out and form a cohesive layer on the surface of the resulting board, the said layer hardening during the subsequent heat treatment and forming an alkaliresistant coating on the surface of the fibre board while, on the other hand, the hardening oil penetrates down into and impregnates the whole of the fibre board. Hardening is effected by heating at a temperature of from about 150 to 200 C.

Example 2 For the manufacture of concrete form board in this case as impregnating agent an alkyd resin having an acid number of 30-50 is applied in an amount of 610% based on the Weight of the dry fibre material. As surface coating resin at cation-active urea-formaldehyde resin having a particle size Within the ranges 50-100 is applied in an amount of 1.55% of the fibre weight.

The alkyd resin is emulsified in water with the aid of a suitable emulsifier, for example an alkali-soap, in a ratio oil:water=1:51:l0. To this emulsion is then added the cation-active resin in the form of a 40% solution, for example.

By mixing, the resin and the oil are precipitated in the form of fine flocs which precipitate is applied to the fibre felt, suitably after the last pair of rolls of the board machine. Owing to their size, the resin-oil-flocs remain on the surface of the felt. When the latter is then subjected to hot-pressing at a temperature of 150-200 C. and a pressure of 15-50 kg./cm. as indicated above, the resin is converted into a hard, resistant surface coating layer and simultaneously the impregnating agent penetrates into the felt throughout its thickness. The pH in the pressing operation is normally maintained within the limits 4-7. Hardening is effected as indicated above.

In this example, as well as in the foregoing, the same result is obtained, if the impregnating oil and the surface coating resin, instead of being supplied simultaneously, are supplied separately.

What we claim is:

1. A process for the manufacture of oil-hardened wood fibre board suitable for use as form board in the casting of concrete wherein the wood fibre material after it is formed into a fibre felt and is still wet is treated with an impregnating agent and is then subjected to a pressing against a polished plate, which comprises: (a) applying to one face only of the wet fibre felt an impregnating agent consisting of a dispersion of a hardenable oil and an alkali resistant thermosetting plastic, (b) hot pressing the impregnated felt against a polished plate on the side of the felt provided with said agent at a temperature sufficiently elevated to harden the impregnated pressed board, (0) the side of the felt facing the polished plate being made acid in reaction at least prior to completion of the pressing step, (d) the viscosity of the hardenable oil in the dispersion being from about 200 to 800 cp. at 20 C., (e) the viscosity of the thermosetting plastic being over 5000 cp. at 20 C., (f) whereby the hardenable oil in said dispersion penetrates the felt and is distributed substantially homogeneously throughout while the thermosetting plastic forms a cohesive water-impermeable alkali-resistant coating on the polished face of the fibre board, thereby producing a board containing from about 3 to 12% of the hardenable oil and from about 0.5 to 10.0% of the thermosetting plastic based on the weight of the dry fibre material in the finished fibre board.

2. The process of claim 1 wherein the hardening oil is selected from the group consisting of linseed oil, tall oil and esters and alkyds of these oils.

3. The process of claim 1 wherein the alkali-resistant plastic is selected from the group consisting of cationactive urea-formaldehyde resins, melamine-formaldehyde resins and mixtures there-of.

4. The process of claim 1 wherein the impregnating oil is applied in the form of an aqueous emulsion containing ammonium compounds as emulsifying agent.

5. The process of claim 1 wherein the plastic is applied dispersed in an aqueous medium in the form of particles having a particle size of from about 5 to microns.

6. The process of claim 1 wherein the hot pressing is effected at a pressure of from about 15 to 50 kg./cm. and at a temperature from about to 200 C.

References Cited in the file of this patent UNITED STATES PATENTS 372,927 Pond Nov. 8, 1887 1,976,433 Cheetham Oct. 9, 1934 2,375,450 Walter May 8, 1945 2,409,629 Heritage Oct. 22, 1946 2,437,931 Bergstrom et al. Mar. 16, 1948 2,632,714 Toomer Mar. 24, 1953 2,654,296 McCorkle Oct. 6, 1953 2,744,013 Dorland May 1, 1956 FOREIGN PATENTS 704,097 Great Britain Feb. 17, 1954 

1. A PROCESS FOR THE MANUFACTURE OF OIL-HARDENED WOOD FIBRE BOARD SUITABLE FOR USE AS FORM BOARD IN THE CASTING OF CONCRETE WHEREIN THE WOOD FIBRE MATERIAL AFTER IT IS FORMED INTO A FIBRE FELT AND IS STILL WET IS TREATED WITH AN IMPREGNATING AGENT AND IS THEN SUBJECTED TO A PRESSING AGAINST A POLISHED PLATE, WHICH COMPRISES: (A) APPLYING TO ONE FACE ONLY OF THE WET FIBRE FELT AN IMPREGNATING AGENT CONSISTING OF A DISPERSION OF A HARDENABLE OIL AND AN ALKALI RESISTANT THERMOSETTING PLASTIC, (B) HOT PRESSING THE IMPREGNATED FELT AGAINST A POLISHED PLATE ON THE SIDE OF THE FELT PROVIDED WITH SAID AGENT AT A TEMPERATURE SUFFICIENTLY ELEVATED TO HARDEN THE IMPREGNATED PRESSED BOARD, (C) THE SIDE OF THE FELT FACING THE POLISHED PLATE BEING MADE ACID IN REACTION AT LEAST PRIOR TO COMPLETION OF THE PRESSING STEP, (D) THE VISCOSITY OF THE HARDENABLE OIL IN THE DISPERSION BEING FROM ABOUT 200 TO 800 CP. AT 20*C., (E) THE VISCOSITY OF THE THERMOSETTING PLASTIC BEING OVER5000 CP. AT 20*C., (F) WHEREBY THE HARDENABLE OIL IN SAID DISPERSION PENETRATES THE FELT AND IS DISTRIBUTED SUBSTANTIALLY HOMOGENEOUSLY THROUGHOUT WHILE THE THERMOSETTING PLASTIC FORMS A COHESIVE WATER-IMPERMEABLE ALKALI-RESISTANT COATING ON THE POLISHED FACE OF THE FIBRE BOARD, THEREBY PRODUCING A BOARD CONTAINING FROM ABOUT 3 TO 12% OF THE HARDENABLE OIL AND FROM ABOUT 0.5 TO 10.0% OF THE THERMOSETTING PLASTIC BASED ON THE WEIGHT OF THE DRY FIBRE MATERIAL IN THE FINISHED FIBRE BOARD. 